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Mammals’ ancestor was not as puny as we thought

THE common ancestor of modern mammals was tiny and shrewlike, living unobtrusively in the shadow of the dinosaurs – or so we thought. A genetic analysis now suggests it may have been more like a small monkey in size.

Nicolas Galtier of the Institute of Evolutionary Sciences in Montpellier, France, begs to differ. With colleagues, he used common features in the genomes of 36 modern mammals to sketch out the genome of the creature from which they descended.

Michael Novacek of the American Museum of Natural History in New York is sceptical, given what the fossil record tells us. But Galtier points out that the fossil record is incomplete. A large mammal ancestor might simply have failed to fossilise.